The present invention relates to an optical reproducing and recording method, that is capable of optically reading or writing beyond a diffraction limit of light by using a near field, and further concerns a recording medium and an optical device.
Conventionally, a recording or reproducing technique using a near field has been disclosed in a magazine xe2x80x9cElectronics, Oct. issue, in 1998, pp. 100-102, (published by Ohm Corp.)xe2x80x9d and in a paper xe2x80x9cApplied Physics Letters, Vol. 73, No.15, published on Oct. 12, 1998, pp. 2078-2080xe2x80x9d.
Referring to FIG. 5, the following explanation describes a reproducing technique using a near field. In FIG. 5, a laser beam 101 is focused by an object lens and is emitted to an optical disk 102. Here, in the optical disk 102, a protection layer 112, a mask layer 113 formed by an antimony film, a protection layer 114, and a recording layer 115 composed of a phase change material such as GeSbTe are deposited in this order on a substrate 111.
In the mask layer 113, the center of a spot of the focused laser beam 101 has a higher temperature, and the opaque center is changed to transparent one so as to form an aperture 103 as a transparent area. The thickness of the protection layer 114 is set such that near-field light 105 generated at the aperture 103 interacts with the recording layer 115.
According to this arrangement, the aperture 103 whose diameter is smaller than a spot diameter appears in the mask layer 113, so that it is possible to read out information recorded in the recording layer 115 from a recording mark 104 through the aperture 103 even if the recording mark 104 is small with a size of 100 nm or less.
However, in the above-mentioned reproducing technique, light is shut off on the mask layer 113 other than the aperture 103, and information is read out from the recording mark 104 merely through the minute aperture 103, resulting in a smaller amount of light from the recording mark 104. Therefore, in the above conventional art, an S/N ratio is reduced so as to cause difficulty in positively reproducing information.
Further, in the conventional art, the minute aperture 103 is used for recording as well, so that an amount of light is reduced and the recording marks 104 cannot be formed with sufficient sizes.
Additionally, in the conventional art, when increasing an amount of light upon recording to form the sufficiently large recording marks 104, the recording marks 104 become too large, so that a high-density recording cannot be achieved.
In order to solve the above-mentioned problems, the objective of the present invention is to provide an optical reproducing and recording method, a recording medium, and an optical device that can achieve a high S/N ratio upon reproducing and recording or can easily form a recording mark by increasing an amount of light received from the recording mark and an amount of light transmitted to the recording mark.
In order to overcome the aforementioned problems, the optical reproducing and recording method of the present invention includes the steps of: emitting a light beam onto a mask layer which is formed on a substrate containing a sample having information and which reduces its transmittance of light due to light or heat; and reproducing or recording the information by interaction between the sample and a near field which appears around an area of the mask layer, the area having transmittance being reduced by the light beam.
Therefore, with this method, light of the near field is generated in the sample and around the area of the mask layer that reduces its transmittance, so that it is possible to realize interaction between the sample and light of the near field, and the interaction generates scattered light from light of the near field based on the information.
In this case, according to this method, it is possible to detect the scattered light from a larger area having a high transmittance of light on the mask layer other than the area in which transmittance of light is reduced, thereby reproducing information of the sample with a high S/N ratio.
In order to solve the aforementioned problems, another optical reproducing and recording method of the present invention adopts a mask layer in which free electrons increase due to light or heat, instead of the mask layer in which transmittance is partially reduced by a light beam.
Hence, with this method, plasmon is pumped in a minute area in which free electrons increase due to a light beam, so that it is possible to write or read information of the sample in a near field, which is generated by the plasmon with high intensity around the minute area. Thus, according to this method, the near field with high intensity makes it easy to write information into the sample, and when reading information from the sample, the near field with high intensity makes it possible to read the information with a higher S/N ratio.
In order to solve the aforementioned problems, the recording medium of the present invention is provided with a recording layer for recording information by radiation of a light beam, and a mask layer, in which transmittance of light is reduced by a light beam so as to form the near field in the recording layer, on a substrate.
This arrangement makes it possible to detect the scattered light from a larger area having a high transmittance of light on the mask layer other than an area in which transmittance of light is reduced, thereby reproducing information of the recording layer with a high S/N ratio.
In order to solve the aforementioned problems, another recording medium of the present invention is provided with a recording layer which records information by radiation of a light beam, and a mask layer in which free electrons are increased by a light beam so as to form a near field in the recording layer by the light beam.
According to this arrangement, plasmon is pumped in a minute area in which free electrons increase due to radiation of a light beam, so that it is possible to write or read information of the recording layer in a near field, which is generated by the plasmon with high intensity around the minute area. Thus, according to this method, the near field with high intensity makes it easy to write information into the recording layer, and when reading information from the recording layer, the near field with high intensity makes it possible to read the information with a higher S/N ratio.
In order to solve the aforementioned problems, the optical device of the present invention has a construction in which the substrate contains the sample; an optical system records or reproduces optical information of the sample being disposed so as to emit a laser beam to the sample; and the mask layer, in which transmittance of light is reduced by the laser beam, is disposed so as to form the near field in the sample by the laser beam.
Therefore, according to this arrangement, when a light beam is emitted onto the mask layer, it is possible to partially form an area in which transmittance of light is reduced on the mask layer, so that light of the near field can be generated around the area on a part of the sample that corresponds to the area.
Hence, this arrangement makes it possible to realize interaction between the sample and light of the near field, so that the interaction can generate scattered light from light of the near field based on information.
Consequently, according to this arrangement, it is possible to detect the scattered light from a larger area having a high transmittance of light on the mask layer other than an area in which transmittance is reduced. Hence, it is possible to reproduce information of the sample with a higher S/N ratio.
For a fuller understanding of the nature and advantages of the invention, reference should be made to the ensuing detailed description taken in conjunction with the accompanying drawings.